caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic

Examples of caffeine in a Sentence

Her doctor told her to avoid caffeine.

Recent Examples on the Web

The first mega-splash came over the summer, with the $20 million-a-year agreement between Monster Energy and college sports’ Big 12 Conference (which includes the caffeine-avoidant Brigham Young University). — Kent Sepkowitz, STAT, 5 Oct. 2026

Overall, the pediatrics academy recommends children ages 12 to 18 limit caffeine to 100 mg a day. — ABC News, 3 Oct. 2026

Though it's already packed with energizing caffeine and circulation-boosting ginseng, the formula takes the brightening powers up a notch with light-reflecting particles that could pass for a full eight hours of sleep. — Madison San Miguel, Allure, 1 Oct. 2026

At almost any hour, someone is settling in for a caffeine fix, a glass of wine, or one more dirty martini. — Condé Nast, Condé Nast Traveler, 29 Sep. 2026

Word History

Etymology

German Kaffein, from Kaffee coffee, from French café

First Known Use

circa 1823, in the meaning defined above

Phrases Containing caffeine

• caffeine-free

Rhymes for caffeine

• agin
• alkene
• allene
• ameen
• amin
• arene
• athene
• baleen
• beeline
• benzene
• between
• bromine

Kids Definition

caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter stimulating compound found especially in coffee, tea, cacao, and kola nuts

Medical Definition

caffeine

noun

caf·​feine ka-ˈfēn, ˈka-ˌ; ˈkaf-ē-ən 

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic

caffeinic

ka-ˈfē-nik  ˌkaf-ē-ˈin-ik 

adjective